User module | Login Feature

# User Login Process

## User Story

As a registered user of the application, I require a seamless and secure login experience. Upon initiating the login process, I expect the system to validate my login credentials. In case the provided credentials are accurate, I anticipate a successful login and immediate redirection to the application's home page.

Should the entered credentials prove invalid, I anticipate the system to provide clear communication regarding the unsuccessful login attempt. This communication may involve displaying an error message to indicate that the provided login details are incorrect.

Upon a successful login, I look forward to being promptly directed to the application's home page, granting me access to the features and content reserved for authenticated users. If the login attempt fails, I expect to receive guidance on how to proceed or regain access.

## End

### DAO:
- [x] findUserByEmail

### Service:
- [x] loginUser

### Test:
TestLoginFeature
- [x] testLoginSuccess
- [x] testLoginFailure

## Flow Chart:

```mermaid
graph TD
Start --> UserInitiatesLogin
UserInitiatesLogin --> ValidateCredentials
ValidateCredentials -->|Valid| SuccessfulLogin
ValidateCredentials -->|Invalid| FailedLogin
SuccessfulLogin --> DisplayHomePage
FailedLogin --> DisplayErrorMessage
DisplayHomePage --> End
DisplayErrorMessage --> End

Beginne damit, die im Issue genannten DAO-Methode findUserByEmail, den Service loginUser und die Tests von TestLoginFeature zu finden. Führe zuerst testLoginSuccess und testLoginFailure aus und vergleiche anschließend den Login-Ablauf mit den angegebenen Ergebnissen: Gültige Zugangsdaten sollten die Startseite erreichen, während ungültige Zugangsdaten einen Fehler und Hinweise zur Wiederherstellung anzeigen sollten.

Vom Indexierungsmodell aus dem Issue-Text verfasst.